It's not realy feasible the way you describe it. You'd need to have a screw go through the ejector block either from the top rear at an angle or from the rear (someone posted a pic of this sort of modification). This can be used to block the magazine catch from being actuated. However, in order to ensure that the catch cannot simply be removed with the action closed, you'd have to make it so that the screw also screws into the magazine catch, capturing it. This might require a catch to be made that lacks the groove at the rear of the top half to provide more metal through which the hole would be drilled and tapped. I think it'd likely be easier to go through the rear of the ejector block. One would have to separate the action, back out the screw enough to allow the catch to be depressed, and then remove the magazine in the normal fashion, and then do the reverse to reinstall the magazine. With a standard mag catch, this can also be done using the "COC-Block" component to prevent magazine catch removal.

What this mag lock design is meant to avoid is having to do something like drill through the ejector block in the first place. Except for the "COC-Block", which requires modification of a readily removable and replacable part, it is drop-in. I can literally install or remove the system in a matter of minutes, and make it useable like a standard rifle in even less time (since the third component of the system does not have to be removed to restore function), maybe two minutes. The only tool required is a screwdriver.

Despite this ease of installation and removal, the action does have to be pivoted open, preventing operation, in order for the magazine to be removed, and the same at minimum is true for removal of any component essential to making it so that such opening is required for magazine removal. For California, this meets the letter of the law for what constitutes disassembly of the action.

A method like the one above might well be suited to a ban state that uses a different fixed magazine definition that would make our FAL Mag Lock design non-compliant, but you'd have to check those laws to be sure. I'm only familiar with the California definition.

Not sure I like the name of the "COC-Block" thing, but it sounds interesting. Do you have a link? Maybe they'd sell more if they called it the "Freedom Penetrator" or something...

My son is going to school in CA, so we're trying to figure out what semi-auto rifles he could bring out and still be in compliance with Commiefornia. Like the Vz58 "Liberty," a top-loading FAL would be a possibility if we could fix the magazine without drilling into the receiver, ejector block, etc. and still maintain a pistol grip configuration.

Not sure what the actual legal definition of "disassembly of the action" is in CA to make these legal. Does it mean removing the bolt carrier / bolt from the receiver (as in the Vz58 Liberty) or can you get away with just separating the upper and lower receivers, which would be easy on a FAL?